1. Field of the Invention
The present invention relates to an information display apparatus to display information on the amount of power generation and the like and an information relay apparatus to relay the information, used in a photovoltaic power generation system or the like, an information display method and an information relay method, and an information transmission method.
2. Description of Related Art
As a representative photovoltaic power generation system, a system-interconnection type system which is interconnected to a commercial power system is known. In this system, generally, DC currents generated by a plurality of solar cell strings are collected in a collection box, then supplied to an inverter, and converted into an AC current. The AC current is outputted to the commercial power system. The amount of power generation, the integrated amount of power generation and the like at this time are displayed on a display unit connected to the inverter. The constructions of the inverter and the display unit are briefly classified into the following two types.
The first construction has a control circuit in the inverter main body. The control circuit comprises a microcomputer or the like. The control circuit of the inverter main body drives display means in the display unit in accordance with a signal from an operation switch on the display unit and output power from the inverter.
The second construction has control circuits respectively in the inverter main body and the display unit. The control circuit of the inverter main body sends data on the amount of power generation to the control circuit of the display unit based on output power from the inverter. The control circuit of the display unit drives display means in the display unit based on the received data and setting by an operation switch on the display unit, to display the amount of power generation, the integrated amount of power and the like. Note that the output power from the inverter is referred to as "the amount of power generation" of the photovoltaic power generation system. The integrated amount of power is a value obtained by integration of the amount of power generation.
In both constructions, one display unit is connected to one inverter.
Further, to display the amount of power generation, a specialized power measuring device may be provided independently of the photovoltaic power generation system. In this case, generally, the construction includes a transducer to detect electric power, an analog to digital (A/D) converter to digitize an analog output signal from the transducer, a control computer utilizing a personal computer (PC) or the like, display means using a cathode-ray tube (CRT) and the like.
In the display unit to display the amount of power generation of the photovoltaic power generation system by the above technique, one inverter is connected to only one display unit. Accordingly, in a case where a plurality of solar cells are provided so as to obtain 8 kW as a total output, and the halves of the solar cells as solar cell arrays are respectively connected to an inverter having rated power of 4 kW, the number of inverters is two. Even if the amount of power generation and integrated amount of power in each inverter can be displayed, the sum of power generation and integrated amount of power in the photovoltaic power generation system cannot be displayed.
On the other hand, if a high rated-power inverter is used, the sum of power generation and integrated amount of power in the entire photovoltaic power generation system can be displayed by one display unit. However, as it is necessary to prepare an inverter having a rated power corresponding to the rated output of the solar cells, i.e., the inverter is specifically designed, the cost is higher in comparison with a case using a plurality of lower rated-output inverters. Further, the external size of the inverter increases in proportion to increment in the output capacity, and wide space is required upon installation of the inverter. Further, in correspondence with increment in weight of inverter, the position of installation requires a certain load-bearing capacity, and further, installation operability is degraded. Accordingly, the construction using a plurality of existing low rated-output inverters is desirable.
Further, in a case where a specialized power measuring device is provided, very high-precision measurement is possible by using the specialized device, however, the cost is very high. Further, in this case, it is troublesome to design the transducer and software for the control computer in correspondence with the rated amount of power generation of the photovoltaic power generation system. Especially, if the additional solar cells and that of inverters are provided in the photovoltaic power generation system, much labor is required to change the transducer and the control software.